1. Field of the Invention
This invention relates to adsorbers and more particularly to column adsorbers.
2. Description of the Prior Art
Solid chemical adsorbents such as activated carbons, silica gel, active alumina, and the like have been successfully used in separating fluid materials according to their respective polarities. During the infancy of this technology, liquids were intimately mixed with the solid adsorbent until the adsorption of a particular ingredient was accomplished. The adsorbent was then filtered leaving the desired purified product. Gases, however, were continuously passed through a column packed with the adsorbent and impurities were removed in this manner. Technical advances soon allowed liquids to be passed on a continuous basis through columns containing the adsorbent which was much more economical than the bulk processes.
Adsorption columns have been used for the purification of materials prior to their use in industrial processes; for the recovery of by-products of industrial processes; for the purification of wastes subsequent to disposal; and for a host of other uses. The purification through columns is substantially more advantageous than the bulk processes in that the step of agitating a particular material in the presence of the adsorbent is eliminated along with a separation of the adsorbent from the purified material.
Typically, when it is believed that a particular material can be purified or recovered in an adsorption column, when such recovery or purification has never been accomplished, as in any other technology, it is necessary to experiment with various adsorbents, column heights, column widths, and other variables on a laboratory scale to determine if the process is feasible and to obtain the particular scaling data necessary to reproduce the desired results on a commercial scale. From the laboratory, pilot plant size experiments based on the laboratory runs are conducted to further determine the feasibility and proper sizing of adsorption equipment for the particular purification or recovery process. After satisfactory results have been obtained and adjustments made in sizing and apparatus, the process is then scaled to the commercial level. Although the laboratory and pilot plant experiments are indicative of desirable results which can be achieved on a commercial scale, exact sizing and other adsorption variables are not completely adaptable to direct scale-up to a commercial installation. Thus, an industrial processor may undergo the laboratory and pilot plant scale-ups and build a commercial adsorber and find that it does not necessarily meet his needs. This, among other reasons, has inhibited the use of adsorbers in various industrial processes.
A further reason for the inhibition of manufacturers to install adsorption equipment is the cost of desorption of the adsorbents. In a typical industrial process, the particular material is passed through the adsorbent in the column on a continuous basis. After so much of the impurity or by-product is adsorbed, the adsorbent reaches its saturation point and no longer adsorbs the desired materials. Usually this requires that the process be halted, the columns emptied of adsorbent, and the adsorbent be regenerated by desorption through well-known processes. After desorption the adsorbent is recharged to the column and the process is continued.
In the small scale adsorption systems, i.e. columns which are 4-10 inches in diameter by 5-10 feet high, the adsorbent can be readily supported and the liquid and/or vapor passing through the adsorbent can readily be distributed. Further, the loading and the removal of the adsorbent from the column can be readily accomplished. However, on an industrial scale the columns are usually 6 feet or more in diameter and 10 feet or more in height. The mass alone, of adsorbing material, causes difficulty in loading and removal of the adsorbent and in the regeneration of the spend adsorbent. In some of the large commerical systems, the adsorbent is supported with screening at the bottom of the adsorption column having a mesh substantially greater than the size of the adsorbent. Further, in some instances distributors are placed throughout the length of the column to provide a uniform distribution of material to be treated across the diameter of the adsorber. These distributors are necessarily placed intermittently along the length of the column to prevent channeling of the particular material. Channeling is a phenomenon in which random paths are taken by the material causing it to by-pass adsorbent media. Because of the weight of the adsorbent, problems involved in these systems include the screening, which supports the adsorbent, rupturing and also the distributors along the column length plugging with adsorbent causing the flow of material to be restricted or stopped. Both of these occurences require equipment down time due to the necessity for repairing these clogged distributors and ruptured screens. Further the adsorbent must be removed from the column and stored while repairs are undertaken.
In accordance with the present invention, an adsorber is provided which eliminates the risks involved in scaling units from pilot plant size to very large commercial size installations and allows lower desorption costs, while providing the advantage that the adsorbent may be easily loaded into and removed from the adsorber.
Further, in accordance with the invention, most of the adsorbent may be easily retained and supported in the adsorber while ruptured screens are repaired. By disengaging the distributors from the adsorbent, their clogging potential is minimized. Both of these aspects of the invention result in reduced maintenance cost and equipment down time.